Electrode apparatus



Feb. 12, 1935. w. J. YOUDEN 1,990,758

ELECTRODE APPARATUS Filed Sept. 5, 1935 5 Sheets-Sheet 1 Feb. 12, 1935.w. J, YoupEN 1,990,768

ELECTRODE APPARATUS Filed Sept. 5, 1933 3 Sheets-Sheet 2 Patented Feb.12, 1935 1,990,768

UNITED STATES PATENT OFFICE v ELECTRODE APPARATUS William J. Youden,Yonkers, N. Y., assignor to W. M. Welch Manufacturing Company, Chicago,Ill., a corporation of Illinois Application September 5, 1933, SerialNo. 688,148

7 Claims. (Cl. 2045) The present invention has to do with a devicevestigators to the present time have been of bulb used for determiningthe hydrogen ion concenshape, or have been bulbs with depressions ttration of solutions and relates particularly to hold the sample. All ofthese bulbs required athe electrode used therewith. considerable portionof the sample. Another For the purpose of understanding the origin typeof electrode consisting of a hollow tube with 5 and development ofthepresent device, a brief a thin glass membrane across its end iscapable statement of the early history of glass electrodes of using aslittle as two drops of such sample. and their use is given. Each of theelectrodes used required more skill In the development of means fordetermining in its preparation than the electrode to be dehydrogen ionconcentration, the advent of the scribed herein. 10

quinhydrone electrode greatly facilitated the For the purpose ofexplaining the nature of a measurement of hydrogen ion concentration inglass electrode, a specific application will be used.

many solutions. It eliminated the bulky source When proper aqueoussolutions are separated of hydrogen gas. It also eliminated the diilibya thin glass wall, there exists a difierence in culties with solutionswhich foamed excessively, potential between the two solutions; this dif-15 and the troublesome preparation of electrodes ference, as a rule,bears a Simple relationship which frequently become poisoned anduseless. to the difierence in density of free hydrogen ions Especiallygratifying was the diminished time (hereafter designated by the symbolpH) of the required for equilibrium. The quinhydrone solutions.

electrode was not a, perfect electrode by any If the pH of either ofthesolutions iS known, 20

means, and it had its special utility in acid soluthe pH of t other y beobtai ed by us tions. In practice, it did not give accurate data alreadycompiled from the use of the glas values in solutions more alkaline thanpH 8.5. ectrode.

Repeatedly the question has arisen as to the Notwithstanding that .theglass electrode, like 5 possible interaction of the quinhydrone with theh hydrogen a d th quinhyd n electrode. is material in solution. anelectrometric method, the apparatus usually The glass electrode is nowon trial. The diflip y for measuring eleetl'omotive forces cultyencountered in the glass electrode has been is not u ab The im d te d fiou y nin the preparation of the electrodes themselves countered With theglass electrode, Which p and in the extreme fragility of the electrodes.rates the q is that the glass OfieIS Such a 30 In the device hereinafterdescribed, these dish resistance to h pas a f rent hat advantages arefairly well eliminat d, I addieven a sensitive galvanometeris not equalto the tion, the quahtity of the material required for ta k ofindicating the ineq y of the pp examination has been reduced below oneone- Potentialshundredth of a cubic centimeter. Where a quadrantelectrometer is employed 35 Up to the present time, in th use of thglass in place of a galvanometer, it is found that a. reelectrode, itwould appear that more time has n d c que i nece y. One form of elecbeenused in developing a satisfactory voltagetrometer, however, has beenfound useful for this measuring device thaninproducingasatisfactory P pThat is the Lindemahn electrometer,

40 form of glass electrode. which is rugged, very compact, and requiresno 40 At least-four methods of measuring the voltage levelling. Its v ny m is s small that the have been advocated. Early workers used theentire instrument may be Placed on the Stage usual types of quadrantelectrometers. Then of a microscope Where the movement f t e came themethods which employ a thermionic indicator needle yb Observed (along am valve.- These were very bulky. The construccr e scale) h h an ey piec45 tion of tube equipment in the laboratory a With the introduction intothe system of an also difiicult. electrometer that is sufficientlysensitive to be ac- One investigator used and advocat d th baltuated bythe minute currents passing through listic galvanometer. Other of theinvestigators the walls of the glas Capillary, the p s 01 depended uponother types of galvanom ter satisfactory shielding and insulating thesystem 50 Efiorts have been made to reducethe resistance have become ofparamount importance. Evidentof the electrode system to the point thatth crly if the set-up requires a potentiometer circuit dinarygalvanometer could be used but without in which no deflection of theelectrometer is the great success. indication of perfect balance, theslightest static Most of the electrodes employed by the ineffects mustbe eliminated. The metal box, which 5 is described later and in whichallof the parts of the apparatus are housed, furnishes the shieldingrequired. The switches, which form the control parts of the electrometercircuit and provide means for grounding and charging. the quadrants andthe needle of the electrometer, must bebuilt with proper insulation ofquartz and of bakelite or other similar dielectric substance so as toavoid the slightest leakage of the charges on these parts of theelectrometer while observations arebeing taken. The glass-electrodeset-up that includes the glass electrode, the connecting vessels and theaccompanying calomel .or other half cells, and because it iselectrically connected to the needle of the electrometer, must be wellinsulated by quartz or the like so that, when desired, the charge on theneedle may be maintained at a constant magnitude fora period of time.

With this brief statement concerning the field and the prior art'in thescope of the present invention the plausibility of the various objectswill be recognized.

It is one object of the present invention to provide a new and improveddevice or system for the determination of the hydrogen ion concentrationof solutions and to make a more rugged and compact device for thispurpose than has heretofore been practicable.

Another object of the invention is to provide a new and improvedapparatus for the detection of minute difi'erences in electricpotentials of solutions whereby the hydrogen ion concentration of one ofthose solutions may readily be determined.

Another object of the invention is to provide a special three-circuitswitch having an especially high insulation factor by the use of quartzand bakelite' or other phenol preparation so that the plates of theLindemann electrometer may be charged by a 3" battery or grounded atwill and the needle of the electrometer charged by the glass electrodecell and also grounded at will.

A still further object of the invention is to provide a unique andimproved device in which minute electrical phenomena may be observed andmeasured free from the influence of outside electrical forces or thelike.

These objects, and such other objects as may hereinafter appear areobtained by the novel construction, unique arrangement, and improvedcombination of elements described in the accompanying specification andillustrated in the attached drawings, hereby made a part of thisspecification, and in which:

Figure 1 is a vertical section through a complete device embodying thesubject matter of the present invention, the arrangement being generallyas the apparatus is used;

Figure 2 is a schematic representation of the electric circuits used inthe device illustrated in Figure 1;

Figure 3 is a schematic representation of the circuit employed in theelectrometer shown in' Figures 1 and 2;

Figure 4 is a view in perspective illustrating a typical glass electrodesuch as is used in the present apparatus, and the method of cleansingsuch electrode;

Figure 5 is an enlarged sectional view of the glass electrode shown inFigure 4; and

Figures 6, -7 and 8 are respectively, top, side and end views of thehigh insulation switch employed in the present apparatus.

Like reference characters are used to designate or it may be entirely ofmetal.

similar parts in the drawings and in the description of the inventionwhich follows.

For housing the apparat a box 10 is provided. Such a box may be of winterlined with metal In the present instance, the box or cabinet shownin Figure 1 comprises walls of wood with a metal outer casing 11, ametal inner lining 12, and-a metal bottom 13, the metal forming a shi dfrom foreign electric fields. I;

For convenience in the asse bly of the apparatus and for purposes ofinspection, ,the box is provided with a removable cover or top 14. Thecover or top is also of wood with metal inner and outer plates and 16respectively. The electric circuits to be later described are arrangedon the sides of the box, being placed on panels which are attached toeither side of the box. Stems 1'7 for potentiometer knob 18 extend tothe exterior of the box on one side. One such stem and knob are shown inFigure 1; the view of the others is obstructed by those shown. Pushbuttons 19 and 20 extend through a side of the box at a position abovethe knobs 18. Suitable openings in the walls of the box and throughwhich the stems and buttons project, permit free manipulation thereof.An opening 21 in the top of the box is provided for the eye-piece 22 ofthe microscope 23.

'A window 24 is placed in the side of the box for illuminating theneedle and scale of an electrometer 25 by permitting the reflection oflight in a mirror 26 of the microscope. A millivoltmeter 27 forming apart of the circuit used in the device may be disposed on the under sideof the removable top. Reading of the millivoltmeter is had through awindow 28. Access to the interior of the box from the top, and by meansof a hinged door (not shown) at the front, may be had without disturbingthe assembly of parts because of the orderly arrangement thereof.

In the device described, there are three electric circuits, showndiagrammatically in Figure 2. In the first circuit, a known potential isset up by an ordinary dry cell 29 of one and one-half volts actingthrough fixed resistances 30 and 31 in series with two potentiometers 32connected in parallel and manipulated by the knobs 18.

The fixed resistances 30 and 31 are of twenty ohms and two ohmsrespectively, and the two potentiometers 32 are each twenty ohms. Themillivoltmeter 27 is connected commonly across the terminals of thepotentiometers 32 at the binding posts 33 and 34. The millivoltmeterwhich has proved highly useful has a double scale, the

lower scale reading to three hundred millivolts and the higher scalereading to twelve hundred millivolts. When the high range scale is to beused, the positive lead of battery 29 is transferred to the binding post35 at the extreme right of the panel 36, thus cutting out the twenty ohmresistance 30. The electric circuit just described is completed throughthe metal lining 12 of the cabinet to which one side of thepotentiometers 32 and one side of the battery 29 are grounded. Thebinding post 34 is also grounded to the lining of the cabinet so thatthe millivoltmeter will read the voltage drop across the potentiometers32.

In another circuit including the leads 37 and 38, Figure 2, one pair 39of the electrometer quadrants, Figure 3, is brought to approximatelytwenty-two volts above ground and the other pair 40 to about twenty-twovolts below ground by means oi blocks of B".and C batteries, 41 and 42,acting through the high insulation switch ill) shown in detail inFigures 8, 7 and 8. This switch is capable of charging the quadrants andthe electrometer needle 43 or grounding them as desired by the operator.Grid leaks 44 and 45, Figure 2, are mounted on the high insulationswitch to prevent damage to the electrometer by limiting the flow ofcurrent in case of a short circuit thereacross.

The C"- batteries are included in the twentytwo volt battery blocks 41and 42 so that they may be removed and replaced to change the potentialof the electrometer quadrants by reasonably small units. It has beenfound convenient to connect a one thousand 'ohm rheostat (not shown) ofthe potentiometer type across a C battery (not shown) that is connectedbetween the battery blocks 41 and 42. to place the singlepole switch 46at one side of this parallel arrangement of the battery and rheostat andto connect the contact arm of the rheostat to the ground in place of theground connection shown. In this way, the relative voltages impressed onthe two sets of electrometer quadrants may be adjusted more delicatelythan by inserting or removing units of C batteries.

The third circuit includes the electrometer needle 43, (see Figure 3)and the glass electrode set-up. The needle 43 is connected to asinglepole double-throw switch 47, Figures 2, 6 and 7, having a movablearm 48, so that the needle 43 may be connecigldirst directly to theground, and then to the ground through a' series connection with theglass electrode system. Although this circuit appears to join thecircuit heretofore termed number one, which contains the dry cell 29 andthe variable resistances 32, the E. M. F. of this third circuit opposesthat of the first circuit. Therefore, if the voltages drop across thepotentiometers 32, caused by the current flowing in the first mentionedcircuit, is equal and opposite to the voltage of the electrode system,the position of the needle remains unchanged from that assumed when itis connected directly to the ground.

The high-insulation switches before mentioned, and shown schematicallyin Figure 2, are really combined into one switch with three flexiblearms 48, 49 and 50, see Figures 6, 7 and 8.

A base 51 for the switch is made from a heavy bakelite sheet and ismounted on the shield cabinet 10 by means of studs 52 and screws 53. Thestuds 52 are made of a material adapted to insulate the base from themetal wall of the cabinet. The spring metal strip 48, shown at the lowerleft in Figure 6, is securely held beneath the heads of bolts 54 and 55encased in tubular pillars 56 of quartz that may be cemented in thebakelite plate 51 with litharge or other cement. The other end of screw54 serves as a binding post to which is connected a flexible conductor57 leading to the electrometer needle. This strip 48 carries at itsextended end two tungsten contact points 58 and 59, the first of saidpoints firmly touching a similar contact 60 attached to the end of a rod61 that extends through another quartz pillar 56. A firm contact betweenthe points 58 and 60 is so important that a special adjusting screw 62is provided so that the tension of the spring 48 may be regulated. Tothe other end of the rod 61 is attached a lead 63 connecting terminal 64of the calomel cell 65. If the binding post 54 is electrically connectedto the electrometer needle 43 and contact 60 is electrically connectedto the glass electrode system through the calomel cell 65, theelectrometer needle will of any electric charges.

be charged to the potential developed by the glass electrode set-up whencontacts 60 and 58 are together.

The other contact 59 attached to strip 48 opposes, but does not normallytouch the contact 66 on the end of a shorter spring-metal strip 67mounted on a metal bridge 68. A flexible metal strip 69 is alsoconnected to the metal bridge 68, see Figure 7. This bridge 68 ispermanently grounded to the metal shield of the box by a metal strip 70.

When the button 19, which projects outside of the wall 10 of theshielded box, is pressed inwardly, the rod 71 that is free to move inthe metal sleeve 72 displaces the strip 67 'so that contact 66 touchescontact 59 concurrently to separating contacts 58 and 60. Thisestablishes a direct ground connection to the needle 43 to relieve itWhen the pressure on button 19 is removed, contacts 58 and 60 cometogether again, the ground connection is broken and a charge is restoredon the-electrometer needle. Thus, at the will of the operator, 9. chargecan easily be placed on the electrometer needle or removed therefrom.

The circuit just described comprises strip 48, which is the uppermost ofthe three parallel strips 48, 49 and 50, as illustrated in Figure 7. InFigure 7 it can be seen that strips 49 and 50 are adapted to be commonlypressed by the spring strip 69 to be connected to the grounded bridge68. This double spring strip 69 is manipulated by the push button 20.

The spring strips 49 and 50 are anchored at an end in the same manner asis the strip 48. Quartz bushings 56 are adjacent theanchored ends of thestrips 49 and 50, there being rods 75 and 76 within the bushings and inelectrical contact with the strips. Circuit legs 77 and 78 connect therods 75 and 76 to the binding posts 79 and 80 of the electrometer andhence independently to the pairs of quadrants in the electrometer.

The switches comprising strips 49 and 50 are manipulated for chargingand discharging the quadrants of the electrometer in the same manner asis the switch for charging and discharging the electrometer needle.Normally the free end of the contact strip 50 is in contact with thepositive electrode 81 of one group of B batteries 41 while the contactstrip 49 is in contact with the negative electrode 82 of the group of 3"batteries 42, the positive and negative charges of the batteries being,therefore, spread on the two pairs of quadrants 39 and respectively. Theelectrodes just designated by the reference characters 81 and 82, shownschematically in Figure 2, are mounted on the switch base 51 similarlyto the contact point or electrode 60.

Pressure on the button 20 will ground the strips 49 and and consequentlythe electrometer quadrants to remove the electric charges therefrom. Thehigh resistance grid leaks 44 and 45 are connected in series withelectric circuit including the electrometer quadrants to prebrackets 8'7and are for the support of the calomel cells 65 and 91; the brackets 88and 89 are for the support of the vials 92 and 93 in which the glasselectrode proper 94 is immersed. In each of the four brackets, theconnecting arm to which the supporting cup is attached is made 'ofquartz, thus effectively insulating the glass electrode from the metal.box upon which the tripod rests. The calomel cells 65 and 91 areidentical. Their structure is shown in detail in Figure 2. 7

In the bottom of each of the calomel half cells is a layer of mercury115. Above the mercury are layers of calomel paste and saturated calthetip extends into the vessel 92 containing saturated potassium chloridesolution 101. In this way the sample within the tube 94 is completelyset apart from the external fluid 99 by the thin walls of the capillarytube while contact of the sample is established with the solution 101.The result is the separation of sample and reference buffer by a glassmembrane which is the wall of the capillary tube, and the formation ofan electrical potential across said membrane.

Thus, it is manifestthat an electric cell is set up. The E. M. F.developed between terminals 64 and 102 by the two half-cells actingthrough cium chloride denominated by the reference fi e glass electrode94, when an unknown liquid characters 116 and 117 respectively. Anapertured stopper 118 is inserted in the mouth of the calcium half cellvessels, the apertures accommodating bridges 95 and 96 and theelectrodes 64 and 102. The bridges 95 and 96 extend only far enough intothe vessels to reach the calcium chloride for making electrical contacttherewith, the electrodes, however, extend to the bottom of the vesselswhere an effective contact with the mercury is insured by flattenedsections 119. Flattehed sections 119 are pr ferably made of platinum.Glass rods 120 en elop the metal electrodes 64 and 102 toinsulate t einfrom the half cell layers 116 and 117.

The calomel half cells 65 and 91 are electrically connected to thesolutions in the glass electrode vials 92 and 93 by glass bridges 95 and96 containing either a liquid potassium chloride solution or the usualpotassium chloride and agar agar filler. If desired, simpler half cellswith an acid buffer and quinhydrone in place of the calomel and mercurymay be used.

The structure of the glass electrode will next be described. A thinwalled soft glass test tube is used to prepare a capillary tube 94having a bore 97 not over one-half millimeter in diameter. The thicknessof the wall of the capillary tube will usually average about twentymicrons. The ratio of the wall thickness to the bore diameter issubstantially that of the original tube. The volume of the capillarytube is usually one-hundredths cc. or less.

The electrical resistance of the electrode or the wall of the tube 94 isseveral hundred megohms. The use of special glasses that have been foundparticularly adapted for preparing other types of glass electrodes wouldtend to diminish this value. Because a satisfactory resultmay be hadfrom capillary tubes drawn from soft glass tubes, it is unnecessary toemploy special glasses for all ordinary work performed with the deviceunderdiscussion.

The tube which is but a few centimeters long may be bent into the shapeof an exaggerated s, as shown in Figure 4. No difficulty arises inmaking the necessary bends if the glass is first softened by heat. Asmall electric heater is useful for this purpose. Sharp bends are to beavoided, for if they are avoided, the capillary is practically immunefrom breakage. The capillary sections readily fill themselves whenbrought in contact with the sample of the material to be tested. makespossible the collection of a fraction of a drop of the sample in amanner to avoid the transfer of other material and hence contaminationof the sample of the fluid.

After the tube 94 is filled with a sample of solution to be tested it isplaced so that the bend at 98 rests within the reference fluid 99 whileis contained in the latter, .will be different from the E. M. F.developed when either the reference phthalate solution, or a differentunknown liquid is contained in the capillary. These differences inpotential may be observed by reading the millivolt meter for each changeof liquid at the time a balance is obtained between the potential acrossthe potentiometer and the potential developed by the electrode system.The glass wall of the tube 94 separating the liquids has such a highresistance that only minute currents can float therethrough. It is forthis reason, as well as for the reason that should any appreciablecurrent be taken from the cell the potential thereof would be altered,that the very sensitive electrometer and potentiometer system isnecessary for the measurement of the potential of this cell. i

In making a determination, the capillary tube 94 is first filled with asolution of known acidity and the resulting electromotive force in theglass electrode assembly determined.

A convenient solution for this reference solution is M/20 normalsolution of potassium acid phthalate. The electrode 94 is then removed,washed externally and internally dried, and filled with the unknownsolution.

The electromotive force is again determined/1 and the difference betweenthis value and that of the first.electromotive force obtained. Thisdifference is millivolts, if obtained from the data taken when thesolutions are at 25 C., and when divided by the factor 59.1 gives thedifference in pH between the phthalate solution and the unknown. Thefactor 59.1 is taken from a previously prepared chart.

If the solution which bathes the exterior of the capillary tube is aneutral buffer, the voltage obtained with the phthalate in the capillarytube is in the neighborhood of one hundred eighty millivolts. Solutionsmore alkaline than the phthalate give values less than this and thosemore acid give greater values.

The difference in millivolts, after converting to pH by dividing by. theproper factor, is added to or subtracted from 3.98 (the pH of thephthalate solution), depending on whether the voltage obtained with theunknown is smaller or larger than the voltage set up by the phthalatesolution. It follows that the voltage becomes smaller as the solutionbecomes more alkaline. Near the neutral point, the observed voltage iszero and beyond. this the potential increases in the opposite direction,requiring that the terminals 64 and 102 be interchanged.

A voltage so obtained is marked with the negative sign, and added to thevoltage recorded between the phthalate solution and the solution bathingthe capillary tube. The purpose of using the intermediate solutioninstead of comparing the unknown and phthalate solutions directly byplacing the phthalate in the cup is the elimination of sources of error.It is essentially a method of substitution. In the process of takingdifferences any constant errors which appear in the observed voltageswill disappear, or be automatically cancelled. These errors are such asan inaccurate zero setting of the voltmeter, inequality of the twocalomel half cells or liquid junction potentials at the half cells.

To determine the voltage of an unknown system with the apparatus shownschematically in Figure 2, the switch 103 which is connected to the drycell29 and the switch 46 are closed. The millivoltmeter 27 then assumesa position which may be varied by adjusting the potentiometers 32. Thedouble-pole switch arms 49 and 50 are momentarily thrown to ground bypressing the button 20. This relieves the quadrants of the electrometerof any electric charge. When the button 20 is released, the quadrantsare connected to the battery blocks 41 and 42 for a recharge.

The needle of the electrometer grounded by pressing the push button 19for depressing the grounded contactor 66 against the contaotor 59.Whilethe electrometer needle is grounded, and hence at zero potential,the position of the needle image on the scale in the eyepiece of themicroscope is noted.

Upon releasing the spring strip 67, the needle 39 of the electrometer isautomatically connected through the post 61 with the electrode system,which is in series with the known voltage across the potentiometers 32and the ground. unknown voltage of the electrode system which is inopposition to the potential across the resistance 32 does not cancelthat known voltage, as measured by the millivoltmeter 27, the netunbalanced voltage causes the electrometer needle to take anotherposition. The resistance 32 is then adjusted until the voltage dropthereacross, due to the current from the battery 29, is-just equal andopposite to the potential of the electrode system.

When this is accomplished, there will be no de- :fiection of theelectrometer needle when the grounded contactor spring er is removedfrom the spring 48 to permit the spring id to again become electricallyconnected with the electrode 60 because the electrode 6G is at that timeat ground potential. The voltage of the electrode system is at this timeequal to that shown on the millivoltmeter scale. The sensitivity of theelectrometer is such that the voltage may be easily adjusted to one halfmillivolt. Using a 16 MM objective and a 15m: ocular, a sensitivity often eyepiece divisions for an electromotive force of thirty or fortymillivolts is possible.

The sensitivity of the electrometer increases as the potentials imposedon the quadrants of the electrometer approach the critical valuesfurnished by the makers of the instrument.

The main object of this type of glass electrode has been to obtain arugged and compact electrode assembly rather than to investigate thenature of the glass electrode. No effort has been made to determine thelimitations of glass electrodes. In keeping with the effort to obtain arugged and sturdy piece of apparatus, the apparatus herein describedwas, on one occasion, transported for several hundred miles in anautomobile. Within one hour after the completion of the journey, theapparatus was set up and accurate measurements made therewith.

is next.

If the Another important feature of the invention is the ingeniousarrangement of the electrical system so that all external rheostat knobsand switches are grounded to themetal wall or lining of the cabinet sothat the potential thereof will not be changed when touched by anoperator. Hence, this very sensitive apparatus is unaffected by theoperator in the process of taking measurements. The hands of theoperator naturally rest on the box and .do not introduce to the systernany undesired electrical charges.

What is claimed as new and is desired to be secured by Letters Patent ofthe United States is:

1. For use with a device for determining the ion concentration of asolution, an electrode comprising a capillary tube of a dielectricmaterial and containing the solution during such determination.

2. For use with a device for determining the hydrogen ion concentrationof a solution, an electrode comprising a glass tube of dimensions todraw such solution therein by capillary action and containing thesolution during such determination. v

3. For use with an apparatus for determining the hydrogen ionconcentration of a solution, an electrode comprising a capillary tube ofdielectric material containing such solution, a second solution incontact with only the exterior walls of said capillary tube, a supportfor said electrode and said solutions, and means for insulating saidelectrode and said solutions from said support.

4. An apparatus for determining the hydrogen ion concentration of asolution comprising the combination of a cell having a capillary tube ofdielectric material enclosing such solution, a ves sel containing abodyof saturated potassium chloride solution, a second vessel containing abody of reference solution, a section of the exterior of said capillarytube being in electrical contact with the body of reference solution andan open end of said tube extending into said body of rive-semen:chloride, the potassium chloride solution and the reference solutionbeing of opposite polarity in said cell, a source of electrical energy,means for ascertaining the potential of said source of energy, means formodifying the potential of such source, electrical conductor meansconnecting the reference solution to the side of said source of energyof like polarity, and means for detecting equalization of the potentialof the body of potassium chloride solution and or the other side of saidsource of energy.

5. In an apparatus for determining the hydrogen ion concentration of asolution, 'a cell comprising a capillary tube of dielectric materialcontaining the solution under determination, a vessel containing a bodyof electrical conductor solution, a second vessel containing a body ofreference solution, a section of the exterior of said tube being inelectrical contact with the body of reference solution and an open endof said tube extending into the body of electrical conductor solution,said bodies of conductor solutionand reference solution being terminalsof opposite polarity of said cell, in combination with a source ofelectrical energy of variable potential, means for changing thepotential of said source of energy, means for ascertaining the potentialof said source of energy, electrical conductor means connecting saidbody of reference solution to said source of energy at the side of likepolarity, means for detecting when said body of electrical 'shaped bendtherein for immersion in a conductor solution and the other side of saidsource of energy are of the same potential.

6. Apparatus for determining the hydrogen ion concentration of asolution and comprising a capillary tube of insulating materialcontaining such solution duringdetermination of the ion concentrationthereof, said tube having a U- reference solution.

'7. An apparatus for determining the hydrogen ion concentration of asolution and comprising the combination of a cell having a capillarytube of dielectric material enclosing such solution, a vessel containinga body of saturated potassium chloride solution, a second vesselcontaining a body of reference solution, a section of the exterior ofsaid capillary tube being in electrical contact with the body ofreference solution and an open end of said tube extending into said bodyof potassium chloride,\the potassium chloride solution and the referencesolution being of opposite polarity in said cell, a standard half cell,a conducting bond of potassium chloride solution between the saturatedpotassium chloride in the first vessel and said half cell, a secondstandard half cell of potential equal to that of the first half cell, aconducting bond of potassium chloridesolutionbetween the referencesolution in said second vessel and said second half cell, the whole cellthus formed providing for a given observation an invariable source ofelectromotlve force, and a second source of electromotive force opposingsaid first source, means for ascertaining the potential of said secondsource of electromotive force, means for modifying the potential of saidsecond source, electrical conductor means connecting said second halfcell to the side of like poiarity of said second source of electromotiveforce, and means for detecting equalization or the potential of saidfirst half cell and of the other side of said second source ofelectromotive force.

WILLIAM J. YOUDEN.

